1. Field of the Invention
The present invention relates to orthopedic devices for the stabilization and control of a human knee joint which has been injured. More particularly to provide a knee brace which will permit the user a relatively high degree of freedom in the use of the bones while, at the same time, permitting control of the joint so as to optimize healing and stability.
2. Description of Related Art
Devices for adding support and strength to the knee joint have been known for decades and have taken many different forms. While substantially all of these devices have been purported to have mechanical joints designed to produce a smooth articulation of the mechanical joint that is matched to the behavior of the natural human knee joint, very few have, in fact, done so since most known devices have apparently taken for granted that the relative movement of the femur and tibia is a rotation about a single center of rotation, typically in the center of the knee. However, studies have shown that a single pivot movement does not emulate the relative movement of the femur and tibia, and that to do so a mechanical joint must produce an initial rearward movement of the tibia relative to the femur, through the first 25 degrees of flexion, of approximately 8-9 millimeters, followed by a single axis pivot-type rotational movement as the knee continues to flex through a 125.degree. angle, or for whatever angle may be traversed, as limited by the injury or natural limitations of the wearer.
In U.S. Pat. No. 4,603.690 to Skeen, a sliding pivot knee joint is disclosed which produces a rearward sliding of the tibia relative to the femur for a predetermined distance during an initial range of flexion of the knee from a straight leg position and, beyond this initial range of flexion to, thereafter, provide a rotational movement in a path which is a circular segment. However, this sliding pivot knee joint is designed for use by a person whose knee joint has become so weakened or diseased that a collapse may be precipitated by the accidental shifting of the person's weight, while standing, onto the braced leg. As a result, the joint is designed to automatically lock against hyperextension. and also against unintential folding of the knee joint in the direction it normally flexes, in response to the wearer's weight being loaded onto the joint by a shifting of the person's body weight onto the leg wearing the brace. Plainly, such a characteristic would be highly undesirable in a brace intended to protect a healthy or only mildly injured or recuperating knee joint of an athlete participating in active sports, such as football and basketball, where locking of the knee joint at the wrong time could be potentially hazardous.
In Schmid U.S. Pat. No. 3,552,786, the need for a mechanical joint assembly which will prevent hyperextension but which will not lock up so as to prevent normal flexion is recognized. To this end, Schmid discloses a mechanical joint assembly which will produce an initial rearward sliding of the tibia in relation to the femur followed by a rotative movement through an arcuate path wherein a deliberate degree of play is introduced into the joint which is then compensated for by the provision of a displaceable cam member that is biased by an elastomeric compression member housed in a recess of the cam member. While such a joint effectively prevents a lockup of the joint which would make it unsuitable for use, for example, by an athlete, the deliberate introduction of looseness or play into the joint and the reliance upon a resilient elastomeric compression member to take up such play renders the joint unsuitable for the case of a person whose knee joint has degenerated or is otherwise substantially abnormally functioning. That is, in such a case, instead of requiring the knee to produce a proper movement emulating that of a healthy knee joint, such a malfunctioning knee joint is allowed to execute a different and undesirable movement since the biasing effect of the elastomeric compression member may be overcome so as to enable the cam element to shift by an amount corresponding to the extent of the deliberately imposed play or looseness.
In the present inventor's copending U.S. patent application Ser. No. 089,253, filed Aug. 25, 1987, and its parent U.S. Pat. No. 4,723,539, a multiaxis controlled motion knee orthosis is disclosed which is not prone to the shortcomings of either of the above-mentioned patents in that it contains a joint that is designed to constrain the tibia to slide rearwardly relative to the femur for a predetermined distance throughout an initial range of flexion of the knee from a straight leg position, and, beyond that initial range of flexion, to rotate relative thereto along a predetermined arcuate path irrespective of the loading applied to the joint by the leg of the wearer. In the preferred embodiment for a knee joint described in these cases, end portions of femoral and tibial links are interconnected by a cam means comprised of a pair of cam slots formed in the end portion of one of the links and a respective cam follower engaging therein, and wherein each slot has a straight segment adjoining an arcuate segment of equal radius. Such a knee joint has proved excellent in practice and has obtained wide acceptance and utilization. On the other hand, the use of two such slots as disclosed in these preferred embodiments limits the integral strength of the joint, tolerance precision, and production efficiency. Furthermore, an opening disposed in a cover plate element of the joint (for coacting with a post attached to the tibial link for guidance purposes as well as for preventing binding due to frictional forces) can be a source of joint contamination. In another embodiment disclosed in the present inventor's patent and copending Application, provision is made for cases where an orthopedic injury or deformity calls for a restriction in the permissible flexion and/or extension of the knee joint to assure that the user cannot injure himself or herself by either extending or flexing beyond a desirable limit. This is achieved through the use of a motion limiter formed by a modified outside cover plate that has an extension having an arcuate slot opening for an abutment post. However, such a motion limiter, while effective, has proved quite cumbersome.